The present invention refers to a method with the objective of forming a layer with good electrical conductivity to different dielectric ceramic materials. In particular, the invention refers to a method for providing ceramic components for microwave band applications, e.g. ceramic resonators to be used in duplex filters and in the receiver front end pass filters. The advantages of these ceramic components are their small sizes and their minimal losses and their excellent stability.
Whenever ceramic materials are used in the microwave band, good electrical conductivity, corrosion resistance, and good adhesion of the ceramic surface are required of the coating.
The most commonly used coating methods today are coating by wire paste and chemical coating (wet process). Paste coating is a relatively expensive process. Chemical coating has several phases and may influence the electrical characteristics of the ceramic material. In order to obtain sufficient adhesion, the first etching treatments in the chemical coating process are different when different ceramic materials are used and therefore they have to be established separately for every material. In some cases, it is possible to provide the adhesive layer by sputtering, but this method is difficult in connection with components with deep holes or cavities.
The German application publication DE-3706951 discloses a method concerning metal coating of ceramic materials. According to this method, a thin metal coating is formed on the ceramic material by currentless coating, the metal coating is heat-treated and chemically etched to improve the adhesion, after which the surface of the ceramic material is metal-coated by a currentless coating process. This process includes several phases and different process phases should be applied to different ceramic materials.